Assigning connection (role) throws error

Following scenario:

An entity has a required Contact field. During creation of new items this value should be used for a new connection role.

Flow (last step fails):

> Trigger on item creation
> Initialize variable as string for Role-Id
> Get all Connection Roles
> Find the right role and store ID in variable initialized before
> Create a new Connection record with ID variable set for "Role (from)" "Role (to)"

Issue:

Something seems to be missing and I receive following error if I try to create a new entity Connection:

There are no ConnectionRoleId and AssociatedObjectTypeCode pairs present.

I think I have set all relevant and available fields, but something is missing I guess.

Any help is really appreciated here.

Inputs:

{
 "host": {
 "apiId": "subscriptions/[SUBSCRIPTION-ID]/providers/Microsoft.Web/locations/westeurope/runtimes/europe-001/apis/commondataservice",
 "connectionReferenceName": "shared_commondataservice",
 "operationId": "PostItem_V2"
 },
 "parameters": {
 "dataset": "default.cds",
 "table": "connections",
 "item/statuscode": 1,
 "item/_ownerid_type": "",
 "item/_record2roleid_value": "[ROLE-ID]",
 "item/_record1roleid_value": "[ROLE-ID]",
 "item/_record2id_value": "[CONTACT-ID]",
 "item/_record2id_type": "contacts",
 "item/_record1id_value": "[ENTITY-ID]",
 "item/_record1id_type": "[CUSTOM-ENTITY-TYPE]"
 }
}

Outputs:

{
 "statusCode": 400,
 "headers": {
 "Pragma": "no-cache",
 "x-ms-request-id": "***",
 "Strict-Transport-Security": "max-age=31536000; includeSubDomains",
 "X-Content-Type-Options": "nosniff",
 "X-Frame-Options": "DENY",
 "Timing-Allow-Origin": "*",
 "x-ms-apihub-cached-response": "false",
 "Cache-Control": "no-store, no-cache",
 "Date": "Tue, 01 Oct 2019 13:29:38 GMT",
 "Set-Cookie": "ARRAffinity=****;Path=/;HttpOnly;Domain=commondataservice-we.azconn-we.p.azurewebsites.net",
 "Content-Length": "504",
 "Content-Type": "application/json",
 "Expires": "-1"
 },
 "body": {
 "status": 400,
 "message": "There are no ConnectionRoleId and AssociatedObjectTypeCode pairs present. Entities being connected: ([CUSTOM-ENTITY-TYPE],contact); Entity Records being connected: (null,null); Record1ConnectionRoleName: null, Record2ConnectionRoleName: null. ConnectionRoleIds: [ROLE-ID], [ROLE-ID];",
 "source": "***.crm4.dynamics.com",
 "errors": [],
 "debugInfo": "clientRequestId: ***"
 }
}

Role(To): [ConnectionRole1Id as String] Role(From): [ConnectionRole1Id as String] ConnectedWith: [ContactId as String] ConnectedWithType: contacts ConnectedBy: [CustomEntityId as String] ConnectedByType: custom_entity

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